Apparatus for mixing



- June 15, 1943. M.. P. HOFMANN I APPARATUS FOR MIXING Filed Jan; 30, 1941 2 Shets-Sheet 1 MWIWIQ-IQ-I INVENTOR. MAXIMILLIAN RHOFMANN 4 ATTORNEYS I June 15, 1943. P, HOFMA'NN APPARATUS FbR mxme Filed Jan. 30. 1941 ZShebts-Sheet 2 TFG- u MAXIMILLIAN R- HOFMANN ATTORNEYS Patented June 15, 1943 zszisaa APPARATUS FOR MIXING Maximillian P. Hofmann, Bay Village, Ohio, assignor to The C. Bartlett and Snow Company, Cleveland, Ohio, a corporation of Ohio Application January 30, 1941, Serial No. 376,668

Claims.

This invention relates to an apparatus for mixing, and more particularly to improvements in such apparatus by which materials may be mixed to form stable compositions in the nature of suspensions, dispersions or emulsions.

The problem of mixing and treating materials to form stable emulsions or dispersions occurs requently in many different industries. The problems vary according to the type of materials encountered in the material being treated and many different types of machines have been designed for the specific purpose of meeting certain'specific problems. Frequently such ma chines will have little or no value other than for the particular use or problem for which the machine was designed.

Heretofore, most of such machines in effecting the desired action relied solely on a hydraulic shearing action had by feeding the material radially outwardly through a narrow space or gap defined by relatively moving surfaces respectively on a rotor and a stator. In such machines the usual practice is to feed the material centrally to the rotor which would propel the material outwardly by centrifugal force through such narrow space or gap, the material being discharged from the periphery of the rotor. D e

' which effects the desired reduction in particle size of solids or globule size of liquids and semiliquids necessary to form stable emulsions or dispersions, is had by feeding a thin film of the material through a narrow space or rotor gap defined by relatively moving surfaces respectively on a rotor and stator. The relatively moving surfaces having contact with such film cause one side of the film to move in a direction opposite to the other side of the film due to the adhesion of the film to such surfaces. Such relative movement in the material making up such film causesa reduction in particle size of the particles positioned intermediate opposite surfaces of the film.

In order to effect the desired hydraulic shearing action, it will thus be apparent that it is necessary for the film of material being treated to fill the space between and have contact with both of the relatively moving surfaces on the rotor and stator. In those constructions where the material is fed outwardly over the rotor, this condition cannot be fulfilled. Since the distance between the surfaces defining the rotor gap is constant, a given amount of material which will fill the rotor gap at a radially inward point will not fill the rotor gap at a radially outward point. Accordingly, it will be apparent that as the material is fed outwardly over the rotor surface, such material will lose contact with the relatively moving surfaces and the film will break up into separate parts. With this condition, the desired hydraulic shearing action will not effectively take place.

Moreover, the breaking up of the film as it moves outwardly will result in excessive foaming and aeration of the material being treated by reason of the presence of air between the separated parts of the film. In addition, changes in the speed of rotation of the rotor will change the amount of centrifugal force acting on the material and the speed of movement of the material over the rotor. Due to the effect of variations in centrifugal force, it is practically impossible to control or vary the time in which the material is subjected to the action of the relatively moving surfaces without sacrificing the desired hydraulic shearing action.

One of the principal objects of this invention is to provide an improved apparatus of the character referred to which is adapted for use with a wide variety of materials irrespective of the characteristics of such materials and which is not subject to the defects of the prior art with.

respect to the effect of variations in the centrifugal force had upon variations in the speed of operation.

A further object is to provide a device in which the material being acted upon is periodically and progressively subjected to the shearing action of a plurality of different relatively moving surfaces.

A further object is to provide an apparatus of the character deferred to in which a rotor and stator having a plurality of slottedJntermeshing ribs are employed to present a plurality of relatively moving shearing surfaces successively operable upon the material for effecting the desired action, together with means for causing the material being treated to move radially inwardly with respect to the rotor and stator.

Other objects and advantages of the invention will become apparent during the course of the following description.

To the accomplishment of the foregoing and re at dends, said invention, then, consists of the means hereinafter fully described and particularly pointed out in the claims, the annexed drawings and the following description settin forth in detail certain means and one mode of carrying out the invention, such disclosed means and mode illustrating, however, but one of various ways in which the principle of the invention may be used.

In said annexed drawings:

Fig. 1 is a. vertical sectional view of apparatus constructed in accordance with the principles of this invention;

Fig. 2 is a bottom plan view of the rotor shown in Fig. 1;

Fig. 3 is a sectional view of the rotor, shown in Fig. 2, taken substantially on the line 3-3 of Fig. 4;

Fig. 4 is a sectional view taken substantially on the line 4-4 of Fig. 3;

Fig. 5 is a top plan view of a part of the stator shown in Fig- Fig. 6 is a sectional view of taken on the line 6-6 of Fig. 5;

Fig. 7 is a view similar to Fig. 2 illustrating a modified construction;

Fig. 8 is a view similar to Fig. 5 illustrating a modified construction for use in connection with the modified rotor construction illustrated in Fig. 7;

Fig. 9 is an enlarged partial sectional View taken in the plane of Fig. 1 illustrating the preferred construction and arrangement of the intermeshing ribs;

Fig. 10 is an enlarged horizontal sectional view taken through the intermeshing ribs illustrating the manner in which the material is moved relative to such ribs;

Fig. 11 is a view similar to Fig. 10 showing the parts in a different position; and

Fig. 12 is a partial sectional view taken in the :plane of Fig. 1 illustrating a modified'construc tion.

Referring to Fig. 1 of the drawings, the numeral I designates a vertical drive shaft rotatably mounted by a suitable bearing assembly 2 in a supporting housing 3. A stator composed of two parts and indicated as a whole by the numeral 4 is carried by the supporting housing 3. The stator t comprises an annular shaped bottom part 5 having a suitable threaded connection-6 with a housing 3 and an annular shaped top part I having a suitable threaded connection 8 with the bottom stator element 5. A rotor Q is mounted on the shaft I for rotation therewith and is provided with a threaded connection Ill thereto. A hopper I I is secured to the stator element I and is adapted to feed the material to be treated to an annular space I2 adjacent the inner portion of the rotor 9. The threaded connections 6, 8 and II) provide adjusting features for a purpose to be described.

The shaft I and rotor 9 are adapted to be rotated in a clockwise direction as viewed in Figs. 1

the stator part and 4. The upper surface of the rotor 9 is provided with cut-out portions indicated by the numeral I3 to provide impeller blades I4 so arranged as to assist in the movement by centrifugal force of the material being treated outwardly with respect to the rotor 9. The impeller blades I 4 cooperate with the surface I5 of the stator part 1 to effect a preliminary mixing action on the material being treated. Theblades I4 and surface I5 will effect a cutting and shredding action on large particles of material introduced to the mixing machine. If desired, the surface I5 may be and such cutting or shredding action. The stator part I cooperates with the upper surface of the rotor 9 to provide the inlet side of the mixing machine.

The outer peripheral edge IG of the stator 9 is arranged closely adjacent the inner surface ll of the stator part I to provide a narrow space through which the material will be forced by the centrifugal action of the impeller blades I4. The material upon passing through the space defined by the surfaces I6 and I1 will be subjected to an hydraulic shearing action due to relative movement between the surfaces I6 and I1. Such hydraulic shearing action, as pointed out above and as is well known in the art, is effective to reduce the size of the particles or solids in the material being treated. The centrifugal force imparted to the material by the impeller blades I4 is also operative to force the material under pressure through the outlet of the mixer side defined by the stator part 5 and the under side of the rotor 9.

The material will be forced through such outlet side in a direction radially inwardly with respect to the rotor 9 and against the action of centrifugal force encountered therein in a manner to be described. It will be noted that the surfaces I6 and I! are intermediatethe inlet and outlet sides of the mixer and that the flow direction of the material being treated is reversed as it enters the outlet side inorder for it to reach the annular outlet I8 from which it flows by gravity to the roughened or serrated to increase the turbulence discharge outfall passage I9.

The stator 5 and the under portion of the rotor 9 defining the outlet side of the mixer are respectively provided with intermeshing ribs 5a and ta. The preferred arrangement of the ribs 5a and 9a is best shown in Figs. 2' and 5. As shown, the ribs 5a and 9a are concentric and annular in shape and are equally spaced from each other in a radial direction on the face of the rotor and stator so that when the rotor 9 is operatively positioned with respect to the stator 5 the ribs 5a and 9a will be positioned in intermeshin relation. Upon rotation being imparted to the rotor 9 the ribs 9a will move relatively tothe ribs 5:: and a hydraulic shearing action on the material in the space between facing surfaces of adjacent ribs 5a and 9a will be had. Such action on the material will be substantially of the same characy ter as takes place when the material is forced through the space between the surfaces I6 and IT.

The facing ribbed portions of the rotor 9 and stator 5 provide a tortuous path through which a film or layer of material may be forced by the pressure developed by the top side of the rotor against the action of centrifugal force encoun tered on the lower side of the rotor. Such film provides a continuous column of liquid enabling the pressure to move the material radiallyinwardly with respect to the rotor. As the material is moved radially inwardly; it is subjected to an hydraulic shearing action by the relatively moving surfaces defining the tortuous path through which it is moving. Although this action is sufficiently satisfactory for many materials, it has been found that by providing the ribs 5a and 9:: respectively with slots 5b and 9b materially improved results may be obtained. Such slots are arranged in a manner to be described and are operative to provide an increased mixing effect and to provide inwardly extending passages through which the material may be forced. However, with respect to the use of the term annular rib, it will be understood that shown as having slots in the interest of sim-- plicity. but

it will be understood that such ribs may be provided with. like-formed slots throughout their circumferential length.- As shown in Fig. 2, the slots 91) are out along lines 20 drawn tangential to points equally spaced on the periphery of a circle 2i. By forming the slots so cles 2i, and 23 have a diameter of 2% inches and are each divided into 1.11am. the lines I. and 22 being drawn tangential to the po ts of division. When it is considered that in such a commercial embodiment a rotor having an outer vdiameter of about 4% .inches is provided with 'annular ribs about inch thick and slots, about .02 inch-wide, it will be understood that the actual size of the slots in all the showings has been exaggerated. v The rib length between slots is many times greater than the width of the slots.

in this manner such slots are inclined forwardly with respect to a line extending-radially of the rotor 9. This inclination is in the direction of rotation of the rotor as viewed in Fig. 2 and thus v enables the slots 9b to assist in the movement of the material through the passage formed by the slots 9b. This assistance tends to overcome the effect of the centrifugal force resisting move-' ment of the material through such passage.

The stator slots 5b, shown inrFig. 5, are cut along lines 22 drawn tangential to points equalrelation, the stator slots 5b will be inclined oppositely to the inclination of the rotor slots 9b. With the rotor and stator slots thus oppositely inclined, such slots will intersect at an angle to provide a zig-zag passage through which the material is forced. This passa e will be provided upon movement of the rotor to a position with the radial-inner ends of the slots 9b in connection with the radial outer ends of the slots 5!). It is preferred that the rotor and stator slots be so formed that theyflwill intersect at an angle on the order of about 90- If it is desired to have the slots ment of the material under pressure through the passage formed .by the intersecting slots, then the slots 9b may be out along the line 20a drawn tangential to the circle 2|, such. slots 9b being indicated by dotted lines in Fig. 2. In this case.

the inclination of the slots 9b would be rearwardly with respect to the direction of rotation of the'rotor and would thus add to the effect a similar staggered or zig-zag relation of the intersecting slots. If the inclination of the slots 5b is not reversed and slots 51) as shown in Fig. 5 are employed with slots 91) as shown in dotted'lines in Fig. 2, then such slots will intersect to provide a straight passage tangential to the circle 2| through whichthe material being treated may be forced by pressure radially inwardly by the ribs. In some cases, itmay be desirable to employ a straight passage with the slots 9b formed either as shown in solid lines or in dotted lines as viewed in Fig. 2. However, it will be understood that the preferred practice is to cut the slots 5b and 9b along lines inclined in opposite directions so that they will inters'ect to provide a zig-zag passage through which the material 'In forming the slots at and 5b in a commercial embodiment employing a l inch rotor, the cir- 9b resist'move-' In Figs. '1 and 8 the slots so and 9b are shown as extending in a radial direction. .By forming the slots in this manner such slots are not inclined with respect to the direction of rotation of the rotor 9 and will therefore neither add to nor detract from the effect of centrifugal force tending to resist movement of the material through the passages formed by such slots. In all the showings itwill be noted that only alternate slots extend through all the ribs. This alternate arrangement of the slots is provided in order that the space between the-slots on the inner'ribs will not be too small. The material from the passages which do not extend through all the ribs will'be forced'by pressure and will be frictionally dragged by the surface of the ribs 90 through the space between facing surfaces of adjacent ribs to those passages which extend through all the ribs.

The slots 5b and 9b may be formed either flush with the surfaces of the rotor and stator as shown in Figs. 2 and 5 or may be undercut as shown in Figs. 7 and 8.

' action on the material being treated. After the manner if it is desired to maintain the material is'forced through the passages formed by intersecting slots 5b and 9b, it is forced by pressure through the space defined by the reladraulic shearing actlon similar to that had upon passage of the material between the surfaces i6 and i1. These surfaces together with the facing surfaces of the ribs, provide a control feature for the mixer which functions in a manner to be described.

In order that a better understanding may be I 'had of the manner in which the material is moved with respect to the slotted ribs, reference will now be'had to the showing of Figs. 10

and 11. In Fig. 10 there is illustrated diagrammatically aconstruction in which the'slots in the stator ribs 5a are shown enlarged and connecting with the slots in the rotor ribs 9a to provide zig-zag passages 24 through which the material may be forced radially inwardly by pressure from the periphery of the rotor and stator. In Fig. 11 the position of the same parts are shown after movement of the rotor 9 through a small angle.

have been moved intoa position interrupting the flow of material-through the passage 24. Due to into and out of alignment at an extremely rapid rate. It will thus be apparent that the move-' .ment .of the material through the passage 24 will be periodically interrupted at a rapid rate In this latter showing it will be noted that the solid portions 25 of the ribs 9a rotor.

for the other modifications.

corresponding to the speed of rotation of the It will also be apparent that the solid portions 25 of the ribs 9a will be constantly shearing or clipping a section 28 out of the as such section is moved relatively to the parts 21. The blocked sections of material remaining in the passage 24 will be subjected to the same type of action by the relatively moving surfaces presented by the solid portions 25 of the rotor ribs 9a. In addition to this rubbing action, material will occupy the space 28 between the relatively moving rib parts and while in such space will be subjected to a mixing. and shearing acinto and out of alignment, on the material passing through the slots as is had with the modificationswherein a plurality of ribs 9a and 5a are provided. However, due to the fact that only two ribs are provided, the total number of such clipping actions to which the material is subjected will be less than is the case where a plurality of ribs are employed. In the modification shown in Fig. 12 the material being treated is delivered from the inlet side of the rotor under pressure to the space 32 formed between the rotor 9 and stator 5. From the space 32 the material tion similar to that had between the surfaces l6 and II.

By reason of the zig-zag path 24 provided where the slots are formed as shown in Figs. 10

I and 11, it will be apparent that the direction of movement of the material will be reversed as it moves from one rib to another. Such reversal of movement increases the turbulence of flow in the passage, and, in practice, has been found to provide materially improved results as compared to the modifications wherein the passages are straight.

Since it is the angularrelation of the slots on the movable rotor which will affect the movement of the material inwardly with respect to the rotor, it is to be understood that rotor slots 9b formed to assist movement of the material against the action of centrifugal force maybe employed in conjunction with stator slots 5b regardless of whether such stator slots are inclined with respect to a radial line or not. That is, angularly inclined rotor slots 9b as shown in Fig. 2 may be employed with radial extending stator slots 5b as shown in Fig. 5, if desired.

-Where the slots 9b are inclined as shown in Fig.

2, such slots will give the inwardly flowing material an inward impulse which will cause such material to impinge against the side walls of the stator slots 5!) thereby providing an increased mixing effect. In addition to the various. combinations of slots 5b and 9b which may be employed as described above, it is also to be understood that all of such slots need. not be of the same size and adjacent alternate slots respectively may be made larger and smaller to adapt the machine for use with a larger number of a different materials. 7

Although the rotor 9 and thestator 5 have been thus far described as each having a plurality of annular ribs, it is to be understood that the principles of this invention are capable of being carried out in a construction wherein the stator and rotor are respectively provided with only a single rib. Such a modified construction is shown in Fig. 12 illustrating the rotor 9 as having a single annular rib 9a. and the stator 5 as having -a single annular rib 5a. The ribs 9a and 5a in this construction may be provided with slots through which the material may flow by such ribs in the same manner as described above tion the ribs 5a and 9a'will effect the same type of clipping action, due to movement of the slots In this construc- .the material.

is forced through the slots in the ribs 5a and 9a this showing it will be noted that the sides 9c and 5c of the ribs in and 9a are tapered in order to permit adjustment of the space 28 between such ribs to compensate for wear by the material being acted upon. In the event that the facing surfaces defining the space 28 become worn so as to increase the space 28 to a point where the desired action is interferred with, the stator and rotor parts may be taken apart and the top surfaces 29 of the ribs machined or ground down to permit movement of the stator 5 and rotor 9 toward each other to decrease the space 28 between, the tapered sides and 9c of the adjacent intermeshing ribs. In connection with the adjustment to compensate for wear and to vary the space 28, it will be noted that the adjustable mountings 6, 8 and Mini the stator and rotor parts enable the necessary adjustments of such parts relativeto each other and the support 3 to effect an adjustment of the clearance between the surfaces l6 and I1 and the space 28 in order to secure'a proper'mixing action of For a 4 inch rotor as described above, best results will be obtained by maintaining the clearance 28 not greater than .005 inch.

It is believed that the operation of the apparatus will be apparent from the foregoing, and it will be sufiicient to point out that the material to be mixed is first introduced through the hopper ll into the space l2 from which it is moved outwardly by centrifugal force and the action of the blades M. The pressure developed by the blades l4 will then move the material through the space defined by the surfaces l6 and I] and thence through the slots or passages 24 where it is subjected to the intermittent shearing and rubbing action -of the relatively moving parts 25 and 21 and of the relatively moving surfaces of the ribs in and 9a. The material being under pressure as it reaches the inner ends'of the passages formed by the slots 5b and 91; will then be forced through the space between the surfaces 38 and- 3! before reaching the discharge 18. In this manner, the material is subjected to a threestage treatment in which the top of the rotor 9 and the stator part- 1 cooperate to provide the Such three-stage treatment and the particular arrangement of the stages is extremely important to successful operation of the apparatus.

The first stage is particularly desirable in order,

the facing portions of the ribs as a. check to retard the free flow of the material the material is forced through a space of con- I stantly diminishing cross-sectional area. Since movement of the material inwardly to the discharge ill will beresisted by centrifugal force encountered between the stator part and rotor 9, it will be apparent that the slots 5b and 9b' andother spaces between such parts will be 1 maintained filled with fluid. The defects of the prior art due to feeding the material through a space of constantly increasing cross-sectional area are thereby avoided.

The centrifugal force developed by a rotor may be represented as a function of the mass of material being acted upon by the rotor and the speed of the'rotor. In those constructions where the material flows outwardly with respect to the rotor, an increase in the speed of the rotor will increase the centrifugal force and cause the material to be moved outwardly at a more rapid rate, and such material will be subjected to the mixing action for a. shorter period of time. Since it is the surface tension of the material being acted on which resists. movement of the material with respect to the rotor, the time in which the material is subjected to the mixing action will also be affected by the viscosity of the material. That is, materials having .a high viscosity will not move through such a construction as rapidly as materials having a low viscosity, and, for a given speed of operation, the material which will be passed through such a machine will vary considerably according to the viscosity ofthe material being acted upon.

The arrangement of the rotor 9 with respect to the stator parts 5 and I provides a novel control feature in the present construction. The rotor 9 is arranged with respect to the stator part I to accommodate a greater mass of material on the top orinlet side of the rotor 9 than is present in the space between the rotor 9 and stator part 5. The greater mass on the top side of the rotor cancels out the mass of material on the'bottom side of the rotor and enables suchgreater mass of material to force the smaller mass of material through the outlet side of the mixer against the action of the centrifugal force encountered therein. By this arrangement an advantage is gained in that the proper mixing action is not effected by changes in speed of the rotor and viscosity of the material as in the case of a construction The facing surfaces 30 and 3|, together with So and 8a, act

through the outlet side of the mixer inaddition to the hydraulic shearing action to which they subject the material. Actual working conditions have shown that this check upon the inward flow of material with respect to the outlet side of the rotor 9 is a material factor with respect to the mixing action of the apparatus. The adjustable mountings 6, 8 and I0 permitting adjustment of the stator parts! and I and the rotor part 9 relative to each other provide a control with respect to the desired mixing action to be had and the amount, of material which will be deliveredthrough the machine. By adjusting the parts to vary the space between the surfaces 30 and 3! and.

the space between the ribs 9a and 5a, the check or retarding action upon the flow of material with respect to these surfaces may be varied to effect a desired change in the mixing action for a given material. Adjustments between these parts may also be made to vary the mass of material respecwhere the material is merely fed outwardly with respect to a rotor by the action of centrifugal force. In commercial embodiments of the apparatus of thisinvention, it has been found that for a given speed of operation there will be no change in the quantity of material flowin through the machine although the viscosity of the material being acted upon is changed. 'I'he material is subjected tothe same mixing action regardless of the viscosity of the material. It has also been found that an increase in speed of operation willcause an increased mixing efiect although such increase in speed will cause a larger amount or material to be fed through the mixer. Increases in speed of operation to give an increased output do not thereby interfere with the desired mixing action as in those cases where the material fed outwardly with respect to the rotor.

tively on opposite sides of the rotor to vary the discharge of the apparatus. Such adjustments will varythe mass on the top side of the rotor 9 with respect to the mass of material on the lower side of the rotor 9 and thereby vary the force available for moving the material with respect to the lower. side of the rotor 9.

The apparatus described abovewill be found extremely useful in reducing the particle size of solids to colloidal dimensions in the formation of suspensions. The apparatus will also be found useful in effecting the complete dispersion of one phase of material in another in the formation of dispersions and/or emulsions. The apparatus, as indicated above, is usable for a wide variety of materials without change or necessity of fine adjustment and may be readily used in the preparation of food mixtures, the mixing of medicines, the preparation of industrial and chemical compounds, the blending of oils and in practically any case where it is desired to form a stablesuspension, dispersion or emulsion.

Apparatus constructed in accordance with-"the disclosure herein has been employed successfuliy in producing homogenizations of milk,.and icecream, and emulsions of parafline, cottonseed, kerosene and other materials using both soaps and gums as protective colloids. .Colloidal sulphur having an average particle size of onehalf micron has been produced in a single pass through the mill notwithstanding conventional mills have been found incapable of producing such a reduction in several passes. In addition.

the mill has produced stable dispersions of carbon black, solids, dyes, colors, etc., in a single pass.

Other modes'of applying the principle of my invention may be employed instead of the one explained, change being made as regards the means and the steps herein disclosed, provided those stated by any of the following claims or their equivalent be employed.

I therefore particularly point out and distinctly claim as my invention:

1. In apparatus of the character described, a-

mixing unit comprising a support, and a rotor and a two part stator carried by said support, one of said stator parts cooperating with one side of said rotor to provide a mixer inlet side, a pillrality of impeller blades on the inlet side of said rotor, the peripheral portion of said rotor being operatively arranged with respect to said stator through said outlet side under pressure against the action of centrifugal force encountered.

therein, said stator and the outlet rotor side having facing flat annular surfaces positioned radial- 1y inwardly of said intermeshing ribs'for effecting a final shearing action on the material being treated.

2. Apparatus of the character described, comprising a rotor and a stator arranged with respect thereto to provide an inlet side on one face of said rotor and an outlet side on the other face of said rotor, a plurality of impeller blades on the inlet side of the rotor, the peripheral portion of said rotor being operatively arranged with respect to said stator to effect a shearing action on material forced therebetween by said impeller blades, said stator and the outlet side of said rotor respectively having a plurality of ribs in intermeshing relationship, said ribs having cut-out portions operative when in alignment to provide a passage extending substantially radially inwardly of said rotor from the periphery thereof, said impeller blades being operative to force material inwardly through said passage under pressure, said stator and the outlet side of said rotor being provided with facing flat annular surfaces positioned radially inwardly of said intermeshing ribs for effecting a final shearing action on the material being treated.

3. In apparatus of the character described, mixing unit. comprising a support, and a rotor and a two part stator carried by said support,

one of said stator parts cooperating with one side of, said rotor to provide a mixer inlet side, a plurality of impeller blades on the inlet side of said rotor, the other of said stator parts cooperating with the other side of said rotor to provide a mixer outlet side and respectively provided with a plurality of annular intermeshing ribs, said impeller blades being operative to force material radially inwardly through said outlet side under pressure against the action of centrifugal force encountered therein.

4. Apparatus of the character described comprising, a rotor and a stator, arranged in a relation with respect thereto, to provide an inlet side on one face of said rotor and an outlet side on the other face of said rotor, said stator and the outlet side of said rotor respectively having ribs in intermeshing relationship, and a plurality of impeller blades mounted on the inlet side of said rotor, said blades being operative upon rotation of said rotor to force material outwardly from said inlet side.

5. In apparatus of the character described, the combination of a rotor member having a disclike projection thereon having opposed faces and a stator embracing said rotor in close proximity to the opposite faces of said disc-like portion, said assembly provided with an inlet centrally of the first face of said disc-like projection and an outlet centrally of the second face of said disc-like projection, a plurality of impeller means carried by the said first face and so arranged as to constitute a centrifugal pump in the space between said first face and adjacent stator parts, and oppositely directed projections, arranged in over-lapping relation, carried by said second face and adjacent stator parts respectively.

P. HOFMANN. 

